Methods of treating ocular diseases using derivatives of lipoic acid

ABSTRACT

Methods of treating ocular diseases using dithiol compounds, their derivatives, and pharmaceutically acceptable salts thereof are disclosed. In particular, methods using dithiol compounds that comprise derivatives of lipoic acid are described. The dithiol compounds are especially useful for treating ocular diseases such as presbyopia and cataract.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Nos. 61/187,005; 61/187,018; 61/187,023; 61/186,986; 61/187,028; 61/187,033; 61/187,039; 61/186,940; each of which was filed on Jun. 15, 2009, and U.S. Provisional Application Nos. 61/224,930 filed Jul. 13, 2009, 61/235,051 filed Aug. 19, 2009; 61/237,912 filed Aug. 28, 2009; and 61/242,232 filed Sep. 14, 2009.

Each of these applications is incorporated herein by reference in its entirety and for all purposes.

BACKGROUND OF THE INVENTION

As we age, our lenses undergo physiological changes that make it more difficult to focus on near objects. That is why nearly everyone requires reading glasses, even as early as age 35-40. The ability of the eye to change focal power, also known as accommodative amplitude, decreases significantly with age. The accommodative amplitude is 20 diopters in children and young adults, but it decreases to 10 diopters by age 25 and to ≦1 diopter by age 60. The age-related inability to focus on near objects is called presbyopia. All of us will develop presbyopia and will require corrective lenses unless a new treatment is found.

Both presbyopia and cataract are age-related and may share common etiologies such as lens growth, oxidative stress, and/or disulfide bond formation.

There is a need for agents, compositions, and methods for combating ocular disease, including presbyopia and/or cataract.

BRIEF SUMMARY OF THE INVENTION

In one aspect, a compound is provided having the structure of Formula I or pharmaceutically acceptable salt thereof:

In Formula I and I-NC, each of X and Y can be sulfur, selenium, or a sulfonic group. In one embodiment, X and Y are both sulfur. In another embodiment, one of X and Y is sulfur, and the other is sulfur or selenium. R₁₉ is substituted or unsubstituted alkylene. Each of R₂₀, R₂₁ R₃₀, and R₃₁ is independently hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted heterocycloalkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl. Z is N or O. Variable m is 0 or 1, wherein if Z is N, then m is 1, and if Z is O, then m is 0. In one embodiment, R₃₀ and R₃₁ together form a single bond (thereby creating a structure of Formula I) or are they are substituents joined together to form a heteroocyclic ring including X and Y.

In another embodiment, a compound of Formula I, or a pharmaceutically acceptable salt thereof, is employed for pharmaceutical formulations (including a pharmaceutically acceptable excipient) and/or methods of treating ocular disease, e.g., presbyopia or cataract.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the accommodative amplitude in diopters (D) of an untreated human lens as a function of age in years. Borja, D et al. 2008. Optical Power of the Isolated Human Crystalline Lens. Invest Ophthalmol Vis Sci 49(6):2541-8. Borja et al. calculated the maximum possible accommodative amplitude of each measured lens power data point (n=65). As shown, there is good agreement between the age-dependent loss of accommodation and the maximum amplitude of accommodation calculated from the isolated lens power.

FIG. 2 shows a trend graph of the shear modulus versus position in the lens and age. Weeber, H A et al. 2007. Stiffness gradient in the crystalline lens. Graefes Arch Clin Exp Ophthalmol 245(9):1357-66. The line at the bottom is the 20-year-old lens; the line at the top is the 70-year-old lens. The modulus increases with age for all positions in the lens. Measurements were taken up to 4.0 mm from the lens centre. The lines are extrapolated to a radius of 4.5 mm (lens diameter 9.0 mm).

FIG. 3 depicts the average opacity (opacimetry) of an untreated human lens as a function of age in years. Bonomi, L et al. 1990. Evaluation of the 701 interzeag lens opacity meter. Graefe's Arch Clin Exp Ophthalmol 228(5):447-9. Lens opacity was measured in 73 healthy subjects between 10 and 76 years of age without slit-lamp evidence of cataract and with a visual acuity of 20/20. These subjects were classified into ten age groups. This study was carried out using the Interzeag Opacity Meter according to the procedure described by Flammer and Bebies (Flammer J, Bebie H. 1987. Lens Opacity Meter: a new instrument to quantify lens opacity. Ophthalmologica 195(2):69-72) and following the suggestions of the operating manual for the instrument.

FIG. 4 depicts a scatter plot of the change in ΔD (micrometers) in the absence (control) and presence of lipoic acid in lens organ culture experiments. The symbol ‡ designates significantly larger changes in ΔD when compared to controls. Statistical values are highly significant at p<0.0001 by unpaired t-test and by Kruskal Wallis test, which compared medians of each data set. The relative change in Young's modulus (E) can be calculated as the cubic value derived from the ΔD of the control divided by the ΔD of the experimental or E fractional change=(ΔD con/ΔDexp)^3.

FIG. 5 depicts a scattergram of the percent of the total protein SH groups in disulfide bonds. Free SH groups were alkylated with 4-acetamido-4′-maleimidylstilbene-2,2′-sulfonic acid (c, 1 μM, 5 μM, 9.6 μM, 50 μM, 96 μM) or 7-diethylamino-3-(4′maleimidylphenyl)-4-methyl coumarin (500 μM, and 500 μM c). Following removal of the first alkylating agent, the S—S bonds were reduced and alkylated with fluorescein-5-maleimide. Absorption spectra were used to calculated total protein (A280 nm), free protein SH (A322 or A384), and protein SS (A490) using the appropriate extinction coefficients. The symbol ‡ indicates statistically significant difference of mean with mean of control (c, p≦0.05). The symbol ** indicates means of 500 μM lipoic acid and the 500 μM control were significantly different from each other (p=0.027).

DETAILED DESCRIPTION OF THE INVENTION

I. Definitions

The abbreviations used herein have their conventional meaning within the chemical and biological arts. The chemical structures and formulae set forth herein are constructed according to the standard rules of chemical valency known in the chemical arts.

Where substituent groups are specified by their conventional chemical formulae, written from left to right, they equally encompass the chemically identical substituents that would result from writing the structure from right to left, e.g., —CH₂O— is equivalent to —OCH₂—. In other words, no orientation is implied by the direction that the group is written.

The term “alkyl,” by itself or as part of another substituent, means, unless otherwise stated, a straight (i.e., unbranched) or branched chain, or combination thereof, which may be fully saturated, mono- or polyunsaturated (i.e., alkenyl) and can include di- and multivalent radicals (e.g., alkylene), having the number of carbon atoms designated (i.e., C₁-C₁₀ means one to ten carbons). Examples of saturated hydrocarbon radicals include, but are not limited to, groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl, sec-butyl, (cyclohexyl)methyl, homologs and isomers of, for example, n-pentyl, n-hexyl, n-heptyl, n-octyl, and the like. An unsaturated alkyl group is one having one or more double bonds or triple bonds. Examples of unsaturated alkyl groups (i.e., alkenyl groups) include, but are not limited to, vinyl, 2-propenyl, 2-isopentenyl, 2-(butadienyl), 2,4-pentadienyl, 3-(1,4-pentadienyl), ethynyl, 1- and 3-propynyl, 3-butynyl, and the higher homologs and isomers. An alkoxy is an alkyl attached to the remainder of the molecule via an oxygen linker (—O—). An alkthio is an alkyl attached to the remainder of the molecule via a sulfur linker (—S—).

The term “heteroalkyl,” by itself or in combination with another term, means, unless otherwise stated, a stable straight or branched chain, or combinations thereof, consisting of at least one carbon atom and at least one heteroatom. A “heteroatom” includes oxygen (O), nitrogen (N), sulfur (S), phosphorus (P), selenium (Se) and silicon (Si), wherein N and S may optionally be oxidized, and N may optionally be quaternized. A heteroatom(s) may be placed at any chemically acceptable position including an interior position, the position at which the alkyl group is attached to the remainder of the molecule (the proximal end), or at the distal end (e.g., for heteroalkylene groups). Examples include, but are not limited to: —C(O)R′, —C(O)NR′, —NR′R″, —OR′, —SR′, and/or —SO₂R′, and —CN. Up to two heteroatoms may be consecutive, such as, for example, —CH₂—NH—OCH₃.

The terms “cycloalkyl” and “heterocycloalkyl,” by themselves or in combination with other terms, mean, unless otherwise stated, cyclic versions of “alkyl” and “heteroalkyl,” respectively. Examples of cycloalkyl include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl,. Examples of heterocycloalkyl include, but are not limited to, piperidinyl, piperazinyl, morpholinyl, tetrahydrofuranyl, and tetrahydrothienyl.

The term “aryl” by itself or in combination with another term, means, unless otherwise stated, a polyunsaturated, aromatic, hydrocarbon group, which can be a single ring or multiple rings (preferably from 1 to 3 rings) that are fused together or linked covalently. A fused ring aryl refers to multiple rings fused together wherein at least one of the fused rings is an aryl ring.

The term “heteroaryl” by itself or in combination with another term, means, unless otherwise stated an aryl group (as defined above) containing one to four heteroatoms (as defined above). Thus, the term “heteroaryl” includes fused ring heteroaryl groups, which are multiple rings (e.g., 5 and/or 6-membered rings) fused together wherein at least one of the fused rings is a heteroaromatic ring. A heteroaryl group can be attached to the remainder of the molecule through a carbon or heteroatom. Non-limiting examples of aryl and heteroaryl groups include phenyl, naphthyl, pyrrolyl, pyrazolyl, imidazolyl, pyrazinyl, oxazolyl, thiazolyl, furyl, thienyl, pyridyl, pyrimidyl, purinyl, benzothiazolyl, benzimidazolyl, indolyl, isoquinolyl, quinoxalinyl, 5-quinoxalinyl, and quinolyl.

For brevity, the term “aryl” when used in combination with other terms (e.g., aryloxy, arylthioxy, arylalkyl) includes both aryl and heteroaryl rings as defined above. Thus, the term “arylalkyl” is meant to include those radicals in which an aryl group is attached to an alkyl group (e.g., benzyl, phenethyl, pyridylmethyl, and the like) including those alkyl groups in which a carbon atom (e.g., a methylene group) has been replaced by, for example, an oxygen atom (e.g., phenoxymethyl, 2-pyridyloxymethyl, 3-(1-naphthyloxy)propyl, and the like).

For any of the above groups—alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, and heteroaryl—the corresponding divalent radical may be referred to with the suffix -ene.

Regarding size, the non-cyclical groups (alkyl and heteroalkyl) typically have 1 to 24 atoms, preferably 1 to 10 atoms, more preferably 1 to 8 atoms (referred to as “lower” substituent group). The cyclical groups (cycloalkyl, heterocycloalkyl, aryl, and heteroaryl) typically have from 3 to 8 members, preferably 4 to 8 members, more preferably 5 to 7 members.

Any of the above groups—alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, and heteroaryl—may be unsubstituted or substituted. Exemplary substituents are described below. Further, the substituents themselves may also be unsubstituted or substituted.

A “substituent group,” as used herein, means a group selected from the following moieties:

-   -   (A) —OH, —NH₂, —SH, —CN, —CF₃, —NO₂, oxo, halogen, unsubstituted         alkyl, unsubstituted heteroalkyl, unsubstituted cycloalkyl,         unsubstituted heterocycloalkyl, unsubstituted aryl,         unsubstituted heteroaryl, and     -   (B) alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, and         heteroaryl, substituted with at least one substituent selected         from:         -   (i) oxo, —OH, —NH₂, —SH, —CN, —CF₃, —NO₂, halogen,             unsubstituted alkyl, unsubstituted heteroalkyl,             unsubstituted cycloalkyl, unsubstituted heterocycloalkyl,             unsubstituted aryl, unsubstituted heteroaryl, and         -   (ii) alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl,             and heteroaryl, substituted with at least one substituent             selected from:             -   (a) oxo, —OH, —NH₂, —SH, —CN, —CF₃, —NO₂, halogen,                 unsubstituted alkyl, unsubstituted heteroalkyl,                 unsubstituted cycloalkyl, unsubstituted                 heterocycloalkyl, unsubstituted aryl, unsubstituted                 heteroaryl, and             -   (b) alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl,                 aryl, or heteroaryl, substituted with at least one                 substituent selected from: oxo, —OH, —NH₂, —SH, —CN,                 —CF₃, —NO₂, halogen, unsubstituted alkyl, unsubstituted                 heteroalkyl, unsubstituted cycloalkyl, unsubstituted                 heterocycloalkyl, unsubstituted aryl, and unsubstituted                 heteroaryl.

The terms “halo” or “halogen” by themselves or as part of another substituent, mean, unless otherwise stated, a fluorine, chlorine, bromine, or iodine atom. Additionally, terms such as “haloalkyl” are meant to include monohaloalkyl and polyhaloalkyl. For example, the term “halo(C₁-C₄)alkyl” includes, but is not limited to, fluoromethyl, difluoromethyl, trifluoromethyl, 2,2,2-trifluoroethyl, 4-chlorobutyl, 3-bromopropyl, and the like.

The term “acyl” means —C(O)R where R is a substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted heterocycloalkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl.

The term “oxo,” as used herein, means an oxygen that is double bonded to a carbon atom.

The term “alkylsulfonyl” means a moiety having the formula —S(O₂)—R′, where R′ is an alkyl group as defined above. R′ may have a specified number of carbons (e.g., “C₁-C₄ alkylsulfonyl”).

The substituents can be one ore more one or more of a variety of groups selected from, but not limited to, —OR′, —NR′R″, —SR′, -halogen, —SiR′R″R′″, —OC(O)R′, —C(O)R′, —CO₂R′, —CONR′R″, —OC(O)NR′R″, —NR″C(O)R′, —NR′—C(O)NR″R′″, —NR″C(O)₂R′, —NR—C(NR′R″R′″)═NR″″, —NR—C(NR′R″)═NR′″, —S(O)R′, —S(O)₂R′, —S(O)₂NR′R″, —NRSO₂R′, —CN, and —NO₂. Substituents for the non-aromatic groups (alkyl, heteroalkyl, cycloalkyl, and heterocycloalkyl) may also include, e.g., ═O, ═NR′, and ═N—OR′. Each of R′, R″, R′″, and R″″ can be independently hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted heterocycloalkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl. From the above discussion of substituents, one of skill in the art will understand that the term “alkyl” is meant to include groups including carbon atoms bound to groups other than hydrogen groups, such as haloalkyl (e.g., —CF₃ and —CH₂CF₃) and acyl (e.g., —C(O)CH₃, —C(O)CF₃, —C(O)CH₂OCH₃).

Substituents for the non-aromatic groups may be present in any number from zero to (2m′+1), where m′ is the total number of carbon atoms in the group. Substituents for the aromatic groups (aryl and heteroaryl) may be present in any number from zero to the total number of open valences on the aromatic ring system.

Two or more substituents may optionally be joined to form aryl, heteroaryl, cycloalkyl, or heterocycloalkyl groups. Such so-called ring-forming substituents are typically, though not necessarily, found attached to a cyclic base structure. In one embodiment, the ring-forming substituents are attached to adjacent members of the base structure. For example, two ring-forming substituents attached to adjacent members of a cyclic base structure create a fused ring structure. In another embodiment, the ring-forming substituents are attached to a single member of the base structure. For example, two ring-forming substituents attached to a single member of a cyclic base structure create a spirocyclic structure. In yet another embodiment, the ring-forming substituents are attached to non-adjacent members of the base structure.

The symbol “

” denotes the point of attachment of a chemical moiety to the remainder of a molecule or chemical formula.

Certain compounds of the present invention possess asymmetric carbon atoms (optical centers) or double bonds; the racemates, diastereomers, tautomers, geometric isomers, and individual isomers are encompassed within the scope of the present invention. The compounds of the present invention do not include those that are known in the art to be too unstable to synthesize and/or isolate.

The compounds of the present invention may also contain unnatural proportions of atomic isotopes at one or more of the atoms that constitute such compounds. For example, the compounds may be radio-labeled with radioactive isotopes, such as for example tritium (³H), iodine-125 (¹²⁵I), or carbon-14 (¹⁴C). All isotopic variations of the compounds of the present invention, whether radioactive or not, are encompassed within the scope of the present invention.

Any numerical values recited herein include all values from the lower value to the upper value in increments of any measurable degree of precision. For example, if the value of a variable such as age, amount, time, percent increase/decrease and the like is 1 to 90, specifically from 20 to 80, and more specifically from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30.3 to 32, etc., are expressly enumerated in this specification. In other words, all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

II. Compounds

There are provided agents, compositions, and methods that can prevent, reduce, reverse, and/or slow the rate of lens growth, oxidative damage, and/or disulfide bond formation. In some embodiments, these agents, compositions, and methods can effectively prevent or treat presbyopia and/or cataract. In one embodiment, the agents, compositions, and methods can effectively prevent or treat presbyopia.

A. Dithiol Compounds and Derivatives

In some embodiments, the agents described herein are dithiol compounds or dithiol derivatives. Dithiol compounds contain at least two sulfur atoms, preferably exactly two sulfur atoms, while dithiol derivatives include a selenium or sulfonic group in place of one or more sulfur atoms of a dithiol compound. Thus, in one embodiment, the agent has at least two components, each independently selected from a sulfur atom, a selenium atom, and a sulfonic group. In another embodiment, the agent has at least two components, each independently selected from a sulfur atom and a selenium atom.

In some embodiments, the agents contemplated herein can be cyclical, e.g., a five- or six-membered heterocycle, or non-cyclical. Exemplary five-membered heterocycles (designated by the term “Formula 5” in the compound name) include, but are not limited to:

Exemplary six-membered heterocycles (designated by the term “Formula 6” in the compound name) include, but are not limited to:

Exemplary non-cyclical agents (designated by the term “NC” affixed to the formulae designations) include, but are not limited to:

The agents can be classified in various ways. For example, the agent can be encompassed by any one of the following classification groups:

5A, 5B, 6A, 6B, 6C, 6D, and 6E: “cyclical”

5-NC, 6-NC, and NC: “non-cyclical”

5A, 5B, and 5-NC: “5-membered”

5A and 5B: “5-membered cyclical”

6A, 6B, 6C, 6D, 6E, and 6-NC: “6-membered”

6A, 6B, 6C, 6D, and 6E: “6-membered cyclical”

5A and 5-NC: “potential hydrogenation pair”

6A and 6-NC: “potential hydrogenation pair”

5-NC and 6-NC: “potential hydrogenation products”

5A, 6A, 6D, and 6E: “adjacent thiols”

5A and 6A: “adjacent thiols, saturated ring”

6A, 6D, and 6E: “adjacent thiols, 6-membered cyclical”

5B, 6B, and 6C: “non-adjacent thiols”

5B and 6B: “1,3 thiols”

6A, 6B, and 6C: “dithanes”

6D and 6E: “dithiines”

or the agents can be classified by any individual formula.

In some embodiments, substituents X and Y of any of Formulae 5A-B, 6A-E or NC are independently selected from a sulfur atom, a selenium atom, and a sulfonic group. Preferably, at least one of X and Y is sulfur. In one embodiment, X and Y are both sulfur. In another embodiment, one of X and Y is sulfur, and the other is sulfur or selenium. In yet another embodiment, one of X and Y is sulfur, and the other is selenium. In one embodiment, the compound of any of Formulae 5A-B, 6A-E or NC is a seleno derivative where at least one of X and Y is selenium. Without being bound by theory, it is believed that the selenium atom advantageously helps to overcome redox potential.

In some embodiments, each R group of Formulae 5A-B, 6A-E or NC is independently —H, —OH, —OAc, —OR, —SR′, —CO₂R′, an electron withdrawing group, a linear or branched C₁₋₁₈ alkyl optionally substituted by one or more ether, ester, carboxylic acid, phosphate, amide, and/or amine groups, wherein R′ is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heterocycloalkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl. In some embodiments, each R group is independently —H, —OH, —OAc, —CO₂CH₃, or a linear C₁₋₁₈ alkyl optionally having a distal terminal that is —COOH, —NH₂, —CO₂CH₃, or —CO₂CH₂CH₃. It is understood that, absent further description, the term “R group” in the context of compounds of any of the formulae described herein refers to any of R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆, R₁₇ or R₁₈, R₁₉, R₂₀, R₂₁, R₂₂, R₂₃, R₂₄, R₂₅, R₂₆, R₂₇, R₂₈, R₂₉, R₃₀, R₃₁, R₃₂, R₃₃, and/or R₃₄.

In some embodiments, agents can be prepared by altering the placement of a particular R group. For example, any particular R group can be attached to a carbon adjacent to a thiol group (sulfur atom) or thiol derivative (e.g., selenium or sulfonic group). R₁, R₂, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃, and R₁₄ represent such thiol-adjacent positions. In other embodiments, an R group can be attached to a carbon not adjacent to a thiol group or thiol derivative. R₃, R₄, R₅, and R₆ represent such non-adjacent positions. In yet other embodiments, an R group can be attached directly to a thiol group or thiol derivative. R₁₅, R₁₆, R₁₇, and R₁₈ represent such direct thiol or thiol derivative attachments.

In one embodiment, one, two, or more R groups are —H. In some embodiments of Formula 5-NC and 6-NC, both of R₁₅ and R₁₆ are —H.

In one embodiment, one, two, or more R groups are —OH.

In another embodiment, one, two, or more R groups are —OAc. Without being bound by theory, the addition of an acetate ester (—OAc) is believed to improve corneal permeability, which is especially beneficial for the treatment of presbyopia.

In yet another embodiment, each R group is independently —H, —OH, —OAc, or —CH₃. In another embodiment, one R group is a chain substituent (e.g., substituted or unsubstituted alkyl, preferably a C₁₋₁₈ alkyl), and the remaining R groups are independently —H, —OH, —OAc, or —CH₃.

In one embodiment, the agent has the structure of Formula 6A:

wherein each of R₁, R₂, R₇, and R₈ is —H; and R₃, R₄, R₅, and R₆ are independently selected from —H, —OH, and —OAc.

In another embodiment, one, two, or more R groups are —CO₂R′, wherein R′ is as defined herein for any of Formulae 5A-B, 6A-E or NC. In another embodiment, one, two, or more R groups are —OR′. In some embodiments, the R′ of —CO₂R′ or —OR′ is a lower alkyl group having 1-8 carbons. In one embodiment, —CO₂R′ is —CO₂CH₃.

In some embodiments, the agent can be modified by altering the length of the chain substituent(s). Without being bound by theory, longer chains are believed to render the compound more hydrophobic, more lipid soluble, and thus more easily transported across the cell membrane. The length of the chain is limited by the lipid membrane width; a chain longer than the membrane width is likely to cause saponification. Shorter chains, on the other hand, and other similarly small substituents such as —OH and —CO₂CH₃, may be useful for preparing agents that are biologically active in the cytosol and do not require membrane permeability. Substituent size and its concomitant effect on solubility also affect formulation considerations. For example, a hydrophobic drug may be more difficult to formulate as an administratable solution, but it may be more easily formulated for sustained release delivery systems.

In one embodiment, the agent includes a linear substituted or unsubstituted C₁₋₁₈ alkyl or heteroalkyl, which are collectively referred to herein as “linear substituents.” The term “branched substituent” refers to substituted or unsubstituted branched C₁₋₁₈ alkyl or heteroalkyl. Without being bound by theory, linear substituents are more commonly found in natural compounds, so agents including linear substituents may be better tolerated by the body. However, branched substituents may also be used. The linear substituent can be, for example, attached to a carbon adjacent to a thiol group (sulfur atom) or thiol derivative (e.g., selenium or sulfonic group). In some embodiments, one or more of R₁, R₂, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃, and R₁₄ is a linear substituent. In other embodiments, one or more of R₃, R₄, R₅, and R₆ is a linear substituent.

In one embodiment, a chain substituent (e.g., substituted or unsubstituted alkyl, preferably a C₁₋₁₈ alkyl) includes an ether, ester, carboxylic acid, phosphate, amide, and/or amine group at the distal terminal of a chain. In one embodiment, the distal terminal is a carboxylic acid or an amine. In another embodiment, one, two, or more R groups are —(CH₂)₂₋₁₀CO₂H or —(CH₂)₂₋₁₀NH₂. Without being bound by theory, it is believed that carboxylic acid and amine terminals provide attachment points for natural amino acids to form peptide amide bonds. For example, the carboxylic acid terminal of exemplary agent lipoic acid is often covalently attached to the amine lysine side chain of the active mitochondrial enzyme. The mitochondrial functionality of lipoic acid is discussed in further detail below.

In another embodiment, the distal terminal of a chain substituent is an ester, e.g., methyl, ethyl, or isopropyl ester. In one embodiment, one, two, or more R groups are —(CH₂)₂₋₁₀CO₂CH₃ or —(CF₂)₂₋₁₀CO₂CH₂CH₃. Without being bound by theory, esterification is believed to be one way to modify the delivery of the pharmaceutical agent since the agent is inhibited from entering the cell until the ester is broken, e.g., by naturally occurring esterases. In this way, an esterified agent can serve as a prodrug that can be converted to an active form, as known in the art.

In one embodiment, the linear substituent is a substituted or unsubstituted linear C₁₋₁₈, C₂₋₁₂, C₂₋₁₀, C₂₋₈, C₂₋₆, C₄₋₆, C₅₋₆, or C₅ alkyl. Exemplary agents including a linear alkyl substituent are provided in Table 1 following, wherein the remaining R groups which are not expressly defined in Table 1 are independently —H, —OH, —OAc, or —CH₃.

TABLE 1 Formula X, Y R 5A; X is S and Y is S R₁ or R₃ is: 5-NC; or —(CH₂)₃₋₁₀CO₂H; 6B —(CH₂)₃₋₁₀CO₂CH₃; or —(CH₂)₃₋₁₀CO₂CH₂CH₃ 5A; X is S and Y is S; R₁ or R₃ is: 5-NC; or X is S and Y is Se; or —(CH₂)₁₋₂CO₂H; 6B X is Se and Y is S —(CH₂)₁₋₂CO₂CH₃; —(CH₂)₁₋₂CO₂CH₂CH₃; or —(CH₂)₂₋₁₀NH₂ 5A X is S and Y is Se; or R₁ or R₃ is: 5-NC X is Se and Y is S —(CH₂)₃₋₁₀CO₂H; 6B —(CH₂)₃₋₁₀CO₂CH₃; or —(CH₂)₃₋₁₀CO₂CH₂CH₃ 6A X is S and Y is S; R₁ or R₃ is: 6-NC X is S and Y is Se; or —(CH₂)₂₋₁₀CO₂H; X is Se and Y is S —(CH₂)₂₋₁₀NH₂; —(CH₂)₂₋₁₀CO₂CH₃; or —(CH₂)₂₋₁₀CO₂CH₂CH₃ 5B X is S and Y is S; R₁ or R₉ is: X is S and Y is Se; or —(CH₂)₂₋₁₀CO₂H; X is Se and Y is S —(CH₂)₂₋₁₀NH₂; —(CH₂)₂₋₁₀CO₂CH₃; or —(CH₂)₂₋₁₀CO₂CH₂CH₃ 6D X is S and Y is S; R₁, R₃, R₅, or R₇ is: 6E X is S and Y is Se; or —(CH₂)₂₋₁₀CO₂H; X is Se and Y is S —(CH₂)₂₋₁₀NH₂; —(CH₂)₂₋₁₀CO₂CH₃; or —(CH₂)₂₋₁₀CO₂CH₂CH₃

Exemplary agent lipoic acid and some derivatives thereof include a divalent linear alkylene functionality with a carboxylic acid terminal:

In one embodiment, the agent is lipoic acid (5-(1,2-dithiolan-3-yl)pentanoic acid), particularly alpha lipoic acid. In another embodiment, the agent is a lipoic acid derivative. Preferred lipoic acid derivatives do not interfere with the natural cellular mechanisms utilizing lipoic acid and/or dihydrolipoic acid. The agents described herein include those having relatively minor modifications to lipoic acid (e.g., altering chain length, replacing a sulfur atom with selenium) such that naturally occurring mitochondrial mechanisms can utilize either lipoic acid or the derivative. Agents having minor modifications may be relatively substitutable for lipoic acid and do not interfere with mitochondrial activity. Thus, in one embodiment, the agent functionally mimics lipoic acid in terms of redox activity and/or mitochondrial activity, but is not structurally identical to lipoic acid. Other agents include those having more major modifications to lipoic acid (e.g., altering chain placement). Such major modifications may render the agent unrecognizable to the mitochondria, thus avoiding interference with cellular mechanisms. In this way, both minor and major modifications can avoid mitochondrial interference. Mitochondrial interference, or the lack thereof, can be verified by in vitro testing according to methods known in the art such as, for example, a JC-1 Mitochondrial Membrane Potential Assay Kit (Cell Tech. Inc.). One of ordinary skill in the art could balance the strength of the reducing agent, which is believed to be responsible for the therapeutic effect, against mitochondrial interference, which might cause adverse effects. Exemplary lipoic acid derivatives include, but are not limited to: 5-(1,2-thiaselenolan-5-yl)pentanoic acid and 5-(1,2-thiaselenolan-3-yl)pentanoic acid.

Without being bound by theory, it is believed that lipoic acid or derivatives thereof, may upregulate antioxidant pathways (e.g., thioredoxin). Key to this upregulation is the Nrf2 response element. See Li, X., Liu, Z., et al. 2008. Lipoamide protects retinal pigment epithelial cells from oxidative stress and mitochondrial dysfunction. Free Radic Biol Med. 44(7): 1465-1474. This suggests that the mechanism of action for lipoic acid and derivatives includes not only its antioxidant properties, but also an upregulation of other enzymes.

In another embodiment, the linear substituent is a linear C₁₋₁₈, C₁₋₈, C₅₋₁₅, C₁₀₋₁₈, or C₁₀₋₁₆, or C₁₂₋₁₄ alkenyl, the alkenyl chain of which can have one, two, three, or more double bonds. Without being bound by theory, linear alkenyls of relatively longer length, e.g., C₁₀₋₁₈, particularly those including a carboxylic acid or ester group, may exhibit advantageous properties similar to a fatty acid group.

Alkenyls, including those of shorter lengths, are also useful, especially for embodiments of Formula NC. For example, in one embodiment, each of R₁₇ and R₁₈ is independently selected from C₂₋₈, C₂₋₆, C₃₋₆, C₃₋₅, or C₃ alkenyl. In another embodiment of Formula NC, R₁₇ and/or R₁₈ is an —SC₂₋₈ alkenyl.

A chain substituent can include more than one substituent. For example, one exemplary agent is cystine (3,3′-disulanedylbis(2-aminopropanoic acid)), which includes both carboxylic acid and amine substituents. In one embodiment, the agent is cystine or a derivative thereof such as the exemplary derivative shown below:

In another embodiment, an R group substituent is an electron withdrawing group, which can decrease the pKa of the agent. Electron withdrawing groups include, but are not limited to halogens (e.g., F, Cl), nitriles (CN), carboxylic acids (COOH), and carbonyls (CO).

In one embodiment, the agent is an allium oil antioxidant or a derivative thereof. Allium oil antioxidants are advantageously natural, nontoxic, and lipid soluble. Some have been studied as potential cytostatic agents for the treatment of atherlerosclerosis, cancer, etc. Without being bound be theory, the cytostatic properties may also provide advantageous efficacy in the context of ocular diseases caused by lens growth, including presbyopia and cataract.

One class of allium oil antioxidants is the dithiines. Exemplary dithiines include, but are not limited to:

Other allium oil antioxidants include, but are not limited to:

In another embodiment, the agent can be a dithiane or a derivative thereof. Without being bound by theory, it is believed that dithianes increase cellular non-protein SH, a primary objective in the treatment of presbyopia. Exemplary dithianes include, but are not limited to:

In one embodiment, the agent is a derivative of dithiothreitol (DTT) such as trans-4,5-dihydroxy-1,2-dithiane, also referred to herein as “non-lethal DTT”:

Both DTT and non-lethal DTT possess potent antioxidant properties, but non-lethal DTT possesses the further advantage of reduced toxicity thereby being more favorable for use in in vivo settings.

B. Amides and Esters

In certain embodiments, the compound is a heterocyclic ester or amide having the structure of Formula I:

wherein X and Y are as defined above, and Z is nitrogen (N) or oxygen (O), and m is 0 or 1, wherein if Z is N, then m is 1, and if Z is O, then m is 0.

R₁₉ is R₂₂-substituted or unsubstituted alkylene, or R₂₂-substituted or unsubstituted heteroalkylene, wherein R₂₂ is independently substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted heterocycloalkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl. In one embodiment, R₁₉ is a substituted or unsubstituted alkylene, e.g., a C₁₋₈, C₁₋₆, C₃₋₅, or C₄ alkylene.

R₂₀ is hydrogen, R₂₃-substituted or unsubstituted alkyl, R₂₃-substituted or unsubstituted cycloalkyl, R₂₃-substituted or unsubstituted heteroalkyl, R₂₃-substituted or unsubstituted heterocycloalkyl, R₂₃-substituted or unsubstituted aryl, or R₂₃-substituted or unsubstituted heteroaryl. R₂₃ is independently —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₂₄-substituted or unsubstituted alkyl, R₂₄-substituted or unsubstituted cycloalkyl, R₂₄-substituted or unsubstituted heteroalkyl, R₂₄-substituted or unsubstituted heterocycloalkyl, R₂₄-substituted or unsubstituted aryl, or R₂₄-substituted or unsubstituted heteroaryl. R₂₄ is independently —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₂₅-substituted or unsubstituted alkyl, R₂₅-substituted or unsubstituted cycloalkyl, R₂₅-substituted or unsubstituted heteroalkyl, R₂₅-substituted or unsubstituted heterocycloalkyl, R₂₅-substituted or unsubstituted aryl, or R₂₅-substituted or unsubstituted heteroaryl. R₂₅ is independently unsubstituted alkyl, unsubstituted cycloalkyl, unsubstituted heteroalkyl, unsubstituted heterocycloalkyl, unsubstituted aryl or unsubstituted heteroaryl. In some embodiments, R₂₀ is hydrogen or an unsubstituted lower alkyl, e.g., methyl, ethyl, propyl, or butyl. In another embodiment, R₂₀ is hydrogen.

R₂₁ is R₂₆-substituted or unsubstituted alkyl, R₂₆-substituted or unsubstituted cycloalkyl, R₂₆-substituted or unsubstituted heteroalkyl, R₂₆-substituted or unsubstituted heterocycloalkyl, R₂₆-substituted or unsubstituted aryl, or R₂₆-substituted or unsubstituted heteroaryl. R₂₆ is independently —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₂₇-substituted or unsubstituted alkyl, R₂₇-substituted or unsubstituted cycloalkyl, R₂₇-substituted or unsubstituted heteroalkyl, R₂₇-substituted or unsubstituted heterocycloalkyl, R₂₇-substituted or unsubstituted aryl, or R₂₇-substituted or unsubstituted heteroaryl. R₂₇ is independently —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₂₈-substituted or unsubstituted alkyl, R₂₈-substituted or unsubstituted cycloalkyl, R₂₈-substituted or unsubstituted heteroalkyl, R₂₈-substituted or unsubstituted heterocycloalkyl, R₂₈-substituted or unsubstituted aryl, or R₂₈-substituted or unsubstituted heteroaryl. R₂₈ is independently unsubstituted alkyl, unsubstituted cycloalkyl, unsubstituted heteroalkyl, unsubstituted heterocycloalkyl, unsubstituted aryl or unsubstituted heteroaryl.

R₃₀ and R₃₁ are each independently selected from hydrogen, R₃₂-substituted or unsubstituted alkyl, R₃₂-substituted or unsubstituted cycloalkyl, R₃₂-substituted or unsubstituted heteroalkyl, R₃₂-substituted or unsubstituted heterocycloalkyl, R₃₂-substituted or unsubstituted aryl, or R₃₂-substituted or unsubstituted heteroaryl. R₃₂ is independently —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₃₃-substituted or unsubstituted alkyl, R₃₃-substituted or unsubstituted cycloalkyl, R₃₃-substituted or unsubstituted heteroalkyl, R₃₃-substituted or unsubstituted heterocycloalkyl, R₃₃-substituted or unsubstituted aryl, or R₃₃-substituted or unsubstituted heteroaryl. R₃₃ is independently —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₃₄-substituted or unsubstituted alkyl, R₃₄-substituted or unsubstituted cycloalkyl, R₃₄-substituted or unsubstituted heteroalkyl, R₃₄-substituted or unsubstituted heterocycloalkyl, R₃₄-substituted or unsubstituted aryl, or R₃₄-substituted or unsubstituted heteroaryl. R₃₄ is independently unsubstituted alkyl, unsubstituted cycloalkyl, unsubstituted heteroalkyl, unsubstituted heterocycloalkyl, unsubstituted aryl or unsubstituted heteroaryl. In some embodiments, R₃₀ and R₃₁ are each independently hydrogen or an unsubstituted lower alkyl. In another embodiment, R₃₀ and R₃₁ are each hydrogen.

In some embodiments, R₃₀ and R₃₁ together form a single bond (thereby creating a structure of Formula I) or are they are substituents (e.g., substituted or unsubstituted alkyl or substituted or unsubstituted heteroalkyl) joined together to form a heteroocyclic ring including X and Y.

It is understood that each substituent on an alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, aryl or heteroaryl may occur multiple times, each occurrence being independently chosen.

It is understood that the position in the heterocycle of Formula I which is vicinal to X can be an asymmetric center. Accordingly, the (R) and (S) enantiomers of Formula I are contemplated for compounds of described herein, as shown following.

Any of the Formulae herein may be similarly designated R and S. Unless specifically indicated to the contrary, the compounds contemplated herein include all optical isomers, regioisomers, enantiomers and/or diastereomers thereof. In one embodiment, the compound is the R enantiomer.

In some embodiments, the compound has the structure of Formula I, provided however that the compound is not lipoic acid.

1. Amides

In some embodiments, the compound is an optionally substituted heterocyclic amide having the structure of Formula II:

wherein R₁₉, R₂₀, R₂₁, R₃₀, R₃₁, X and Y are as defined above.

In some embodiments, the compound of Formula II has the structure of Formula III:

where R₂₀ and R₂₁ are as defined above.

In some embodiments, R₂₁ is R₂₆-substituted alkyl or R₂₆-substituted heteroalkyl, wherein R₂₆ is present in one or more occurrences, and in each occurrence is independently amine, —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₂₇-substituted or unsubstituted alkyl, R₂₇-substituted or unsubstituted cycloalkyl, R₂₇-substituted or unsubstituted heteroalkyl, R₂₇-substituted or unsubstituted heterocycloalkyl, R₂₇-substituted or unsubstituted aryl, or R₂₇-substituted or unsubstituted heteroaryl. In some embodiments, R₂₁ is aminoalkyl, preferably aminoethyl. In some embodiments, R₂₁ is N-substituted aminoalkyl, preferably N-substituted aminoethyl, wherein the pendant amino functionality is in turn substituted with R₂₇ (e.g., (N,N-dialkylamino)-alkyl, preferably dimethylaminoethyl). In some embodiments, R₂₇ is C₁-C₆ alkyl, preferably methyl. In some embodiments, R₂₁ is phosphonoylalkyl, preferably phosphonoylethyl. In some embodiments, R₂₁ is hydroxyalkyl, preferably hydroxyethyl. In some embodiments, R₂₁ is hydroxyalkyl, preferably hydroxyethyl, and R₂₀ is unsubstituted alkyl, preferably C₁-C₆ alkyl, more preferably methyl. In some embodiments, R₂₁ is hydroxyethyl, and R₂₀ is methyl. In some embodiments, R₂₁ is alkyl which in turn is multiply substituted with —OH (e.g., 2,3-dihydroxypropyl), and R₂₀ is hydrogen.

In some embodiments, R₂₁ is R₂₆-substituted or unsubstituted heterocycloalkyl. Exemplary heterocycloalkyl functionalities include, but are not limited to, morpholino and piperazinyl. In some embodiments, R₂₁ is R₂₆-substituted tetrahydropyranyl, preferably 3,4,5,6-tetrandroxytetrahydro-2H-pyran-2-yl). In some embodiments, R₂₆ is multiply substituted with hydroxyl. In some embodiments, R₂₁ is R₂₆-substituted morpholino, wherein R₂₆ is C₁-C₆ alkyl, preferably methyl.

In some embodiments, R₂₁ is R₂₆-substituted or unsubstituted heteroaryl, preferably (1H-imidazol-2-yl)ethyl.

In some embodiments, R₂₁ is R₂₆-substituted heteroalkyl, wherein the R₂₆-substituted heteroalkyl includes a repeating polymeric unit. Exemplary polymeric units in this context include, but are not limited to, polyethylene glycol [(—CH₂—CH₂—O—)_(n), wherein n>1], as known in the art.

In some embodiments, R₂₁ is as defined above, and R₂₀ is C₁-C₆ alkyl, preferably methyl, ethyl or isopropyl, more preferably methyl.

In some embodiments, R₂₁ is R₂₆-substituted alkyl or R₂₆-substituted heteroalkyl, wherein R₂₆ is present in one or more occurrences, and in each occurrence is independently unsubstituted alkyl. In some embodiments, R₂₁ is aminoalkyl, preferably aminoethyl, and R₂₆ is independently present at the pendant nitrogen 0, 1, 2 or even 3 times.

In some embodiments, R₂₀ and R₂₁ are independently hydrogen.

In some embodiments, the compound of Formula III includes an amino acid bound in amide linkage between an alpha nitrogen of the amino acid or a side chain nitrogen of the amino acid, and the acid functionality of lipoic acid, having the structure of either of Formula IVA-IVB following.

Regarding Formulae IVA-B, the term “AA” refers to an amino acid having a side chain nitrogen in amide linkage with the lipoic acid functionality, and R₂₉ is the side chain of an alpha amino acid, preferably a naturally occurring amino acid or homolog thereof. The linkage between the side chain nitrogen of the amino acid “AA” is indicated by the symbol “

” in Formulae IVA. Exemplary amino acids include, but are not limited to, the naturally occurring amino acids and homologs thereof (e.g., diaminoproprionic acid, diaminobutyric acid, ornithine, lysine, homolysine), as known in the art. Both D/L (R/S) stereoisomers of the amino acids are contemplated herein. Further exemplary amino acid amides of lipoic acid having the structure of Formulae IVA-IVB include, but are not limited to, the compounds set forth below:

TABLE 2 Amino acid amides

In some embodiments, a compound is provided as set forth below:

TABLE 3 Active agent amides

2. Esters

In some embodiments, there is provided an optionally substituted heterocyclic-containing ester of Formula I having the structure of Formula V:

wherein R₁₉, R₂₁, R₃₀, R₃₁, X, and Y are as defined above.

In some embodiments of the compound of Formula V or V-NC, R₁₉ is unsubstituted alkylene, preferably C₁-C₆ alkylene, more preferably C₄ alkylene. In some embodiments, R₁₉ is C₁-C₈, preferably C₁-C₆, more preferably C₄ alkylene independently substituted with one or more R₂₂, wherein R₂₂ is as defined herein.

In some embodiments, the compound of Formula V has the structure of Formula VI following, wherein R₂₁ is substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted heterocycloalkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl.

In some embodiments, R₂₁ is alkyl, preferably C₁-C₆ alkyl, more preferably C₁-C₃ alkyl, most preferably C₁, C₂, or C₃ alkyl, examples of which include, but are not limited to, the compounds set forth below:

TABLE 4 Active Agent Alkyl Esters

In some embodiments, R₂₁ is alkyl, preferably C₁-C₆ alkyl, more preferably C₃-C₅ alkyl, most preferably C₃, C₄ or C₅ alkyl, which in turn is multiply substituted with —OH. In some embodiments, R₂₁ is alkyl substituted with 1, 2, 3, 4 or even 5 hydroxyl functionalities. All diastereomeric, enantiomeric and regioisomeric forms of compounds of Formulae V, VI, VI(R), and VI(S) are contemplated herein.

Exemplary compounds according to any of Formulae V, VI, VI(R), and VI(S) include, but are not limited to, the compounds set forth below:

TABLE 5 Active Agent Substituted Alkyl Esters

In some embodiments, R₂₁ is R₂₆-substituted or unsubstituted alkyl or R₂₆-substituted or unsubstituted heteroalkyl, and R₂₆ is independently —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₂₇-substituted or unsubstituted alkyl, R₂₇-substituted or unsubstituted cycloalkyl, R₂₇-substituted or unsubstituted heteroalkyl, R₂₇-substituted or unsubstituted heterocycloalkyl, R₂₇-substituted or unsubstituted aryl, or R₂₇-substituted or unsubstituted heteroaryl.

In some embodiments, R₂₁ is R₂₆-substituted alkyl or R₂₆-substituted heteroalkyl, wherein R₂₆ is independently present in one or more occurrences, and in each occurrence is independently unsubstituted alkyl, preferably methyl. In some embodiments, R₂₁ is aminoalkyl, preferably aminoethyl, and R₂₆ is independently present at the pendant nitrogen 0, 1, 2 or even 3 times. In some embodiments, R₂₁ is a choline substituent in ester attachment with the lipoic acid structure set forth below. The structure may include a counterion, wherein the counterion is any pharmaceutically acceptable counterion capable of forming a salt with the choline lipoate:

In some embodiments, a substituted group substituted with at least one substituent group. More specifically, in some embodiments, each substituted alkyl, substituted heteroalkyl, substituted cycloalkyl, substituted heterocycloalkyl, substituted aryl, substituted heteroaryl, substituted alkylene, substituted heteroalkylene, substituted cycloalkylene, substituted heterocycloalkylene, substituted arylene or substituted heteroarylene within a compound described herein is substituted with at least one substituent group. In other embodiments, at least one or all of these groups are substituted with at least one size-limited substituent group. Alternatively, at least one or all of these groups are substituted with at least one lower substituent group.

C. Salts

The compounds described herein can also be provided as a pharmaceutically acceptable salt. The term “pharmaceutically acceptable salt” includes salts of the active compounds that are prepared with relatively nontoxic acids or bases, depending on the particular substituents found on the compounds described herein. When compounds of the present invention contain relatively acidic functionalities, base addition salts can be obtained by contacting the neutral form of such compounds with a sufficient amount of the desired base, either neat or in a suitable inert solvent. Examples of pharmaceutically acceptable base addition salts include sodium, potassium, calcium, ammonium, organic amino, or magnesium salt, or a similar salt. When compounds of the present invention contain relatively basic functionalities, acid addition salts can be obtained by contacting the neutral form of such compounds with a sufficient amount of the desired acid, either neat or in a suitable inert solvent. Examples of pharmaceutically acceptable acid addition salts include those derived from inorganic acids like hydrochloric, hydrobromic, nitric, carbonic, monohydrogencarbonic, phosphoric, monohydrogenphosphoric, dihydrogenphosphoric, sulfuric, monohydrogensulfuric, hydriodic, or phosphorous acids and the like, as well as the salts derived from relatively nontoxic organic acids like acetic, propionic, isobutyric, maleic, malonic, benzoic, succinic, suberic, fumaric, lactic, mandelic, phthalic, benzenesulfonic, p-tolylsulfonic, citric, tartaric, oxalic, methanesulfonic, and the like. Also included are salts of amino acids such as arginate and the like, and salts of organic acids like glucuronic or galactunoric acids and the like (see, for example, Berge et al., “Pharmaceutical Salts”, Journal of Pharmaceutical Science, 1977, 66, 1-19). Certain specific compounds of the present invention contain both basic and acidic functionalities that allow the compounds to be converted into either base or acid addition salts.

Thus, the compounds of the present invention may exist as salts, such as with pharmaceutically acceptable acids. The present invention includes such salts. Examples of such salts include, but are limited to, hydrochlorides, hydrobromides, sulfates, methanesulfonates, nitrates, maleates, acetates, citrates, fumarates, tartrates (e.g., (+)-tartrates, (−)-tartrates, or mixtures thereof including racemic mixtures), succinates, benzoates, and salts with amino acids such as glutamic acid. These salts may be prepared by methods known to those skilled in the art.

The neutral forms of the compounds are preferably regenerated by contacting the salt with a base or acid and isolating the parent compound in the conventional manner. The parent form of the compound differs from the various salt forms in certain physical properties, such as solubility in polar solvents.

In one embodiment, the counterion ion is the 1,3-dihydroxy-2-(hydroxymethyl)propan-2-aminium cation (i.e., a tromethamine salt):

III. Methods of Use

The agents described herein can be employed in a method including the step of providing an active agent to a cell, either in vitro or in vivo.

The active agents described herein can be employed in a method for treating or preventing oxidation damage to cells. Such a method includes the step of administering a pharmaceutical composition comprising an active agent to a cell, either in vitro or in vivo.

As stated above, the agents can be delivered to cells in vitro or in vivo. In one embodiment, the cells are in vivo. In either case, the cells can be ocular cells, e.g., lens cells. In one embodiment, the agent is delivered to a lens, either in vitro or in vivo. Because oxidative damage has been implicated in other disorders including cancer, the agents may prove useful for administration to any type of cell exhibiting or prone to oxidative damage.

In one embodiment, the compounds described herein can be used in a method for treating ocular disease. Exemplary ocular diseases include, but are not limited to: presbyopia, cataract, macular degeneration (including age-related macular degeneration), retinopathies (including diabetic retinopathy), glaucoma, and ocular inflammations. In one embodiment, the ocular disease to be treated is cataract. In another embodiment, the ocular disease to be treated is treat presbyopia.

The methods preferably utilize a therapeutically effective amount of the active agent. The term “therapeutically effective amount” means an amount that is capable of preventing, reducing, reversing, and/or slowing the rate of oxidative damage. For ocular applications, a therapeutically effective amount may be determined by measuring clinical outcomes including, but not limited to, the elasticity, stiffness, viscosity, density, or opacity of a lens.

Lens elasticity decreases with age and is a primary diagnostic and causative factor for presbyopia. Lens elasticity can be measured as accommodative amplitude in diopters (D). FIG. 1 depicts the average elasticity in diopters of an untreated human lens as a function of age in years. The lower the value of D, the less elastic the lens. In one embodiment, the agents described herein can decrease and/or maintain D at a value that is greater than the D value exhibited by an untreated lens of about the same age. In other words, the agents can keep accommodative amplitude “above the line” depicted in FIG. 1 (the solid line is mean accommodative amplitude). In one embodiment, D is increased and/or maintained at a value about 2, 5, 7, 10, 15, 25, 50, 100, 150, or 200 percent above the line. However, as individual lenses may differ with respect to average values, another embodiment provides any increase in accommodative amplitude, maintenance of accommodative amplitude, or reduction in the rate of decline of accommodative amplitude (i.e., reduction in the rate of decrease in diopters) for an individual lens compared to the accommodative amplitude of the same lens before treatment. Accordingly, in another embodiment, the methods provide an increase in accommodative amplitude of about 0.25 to about 8 diopters, or at least about 0.1, 0.2, 0.25, 0.5, 1, 1.2, 1.5, 1.8, 2, 2.5, 3, 5, or 8 diopters compared to the same lens before treatment.

Lens elasticity can also be measured by the unit of elasticity E. The higher the value of E, the less elastic the lens. FIG. 2 depicts the average elasticity (E) of an untreated human lens as a function of age in years. In one embodiment, the agents described herein can decrease and/or maintain E at a value that is less than the E value exhibited by an untreated lens of about the same age. In other words, the agents can keep lens elasticity “below the line” depicted in FIG. 2. In one embodiment, E is decreased and/or maintained at a value about 2, 5, 7, 10, 15, 25, 50, 100, 150, or 200 percent below the line. However, as individual lenses may differ with respect to average values, another embodiment provides any increase in elasticity, maintenance of elasticity, or reduction in the rate of decline of elasticity (i.e., reduction in the rate of increase in E value) for an individual lens compared to the elasticity of the same lens before treatment.

Therapeutic efficacy can also be measured in terms of lens opacity. Lens opacity increases with age and is a primary diagnostic and causative factor for cataract. FIG. 3 depicts the average opacity of an untreated human lens as a function of age in years. In one embodiment, the agents described herein can decrease and/or maintain opacity at a value that is less than the opacity value exhibited by an untreated lens of about the same age. In other words, the agents can keep lens opacity “below the line” depicted in FIG. 3. In one embodiment, lens elasticity is decreased and/or maintained at a value about 2, 5, 7, 10, 15, 25, 50, 100, 150, or 200 percent below the line. However, as individual lenses may differ with respect to average values, another embodiment provides any decrease, maintenance, or reduction in the rate of increase of opacity for an individual lens compared to the opacity of the same lens before treatment.

Therapeutic efficacy can also be measured as a reduction in the rate of cell proliferation, particularly lens epithelial cell proliferation. Thus, in some embodiments, therapeutic efficacy can be measured by cytostatic effect.

The active agent can be administered as a racemate or as an enantiomer. For example, lipoic acid and its derivatives are preferably administered to include the R form; cystine and its derivatives are preferably administered to include the L form. Synthetic methods to yield a racemate may be less expensive than stereo-specific processes including isolation/purification steps. On the other hand, administering a single enantiomer can lower the therapeutically effective amount, thus decreasing toxicity effects.

The agents described herein are preferably reducing agents. For example, the agents can possess a redox potential E₀′ (V) of about −0.01 to about −1.0, about −0.1 to about −0.5, about −0.2 to about −0.4, or about −0.3. The agents described herein preferably exhibit an acceptable toxicity profile, e.g., a median lethal dose (LD₅₀) of at least 10 μM, at least 20 μM, at least 40 μM, or at least 1 mM. Toxicity can be assessed by any method known in the art such as, for example, viability of human umbilical vein endothelial cells (HUVEC, first passage) using the MultiTox-Fluor assay (Promega) or Live/Dead® assay (Invitrogen). Of course, agents selected as pharmaceutical agents for the treatment of presbyopia should exhibit both antioxidant efficacy (reducing power) as well as a desirable safety profile (low toxicity). Accordingly, in one embodiment, a screening method is provided whereby dithiol compounds or derivatives are tested for reducing power and/or toxicity. In another embodiment, a method includes screening dithiol compounds or dithiol derivatives for their ability to increase lens elasticity either in vitro or in vivo.

The agents described herein preferably exhibit favorable membrane permeability, specifically corneal permeability. Corneal penetration can be measured by methods known in the art, such as, for example, those disclosed in Kim et al. (2005) “Aqueous penetration and biological activity of moxifloxacin 0.5% ophthalmic solution and gatifloxacin 0.3% solution in cataract surgery patients” Ophthalmology 112(11):1992-96. In one embodiment, the agent enters the lens epithelial cells using a naturally occurring transport mechanism. For example, lipoic acid and cystine enter lens cells via specific plasma membrane symporters and antiporters. By using lipoic acid, cystine, or derivatives thereof, one can utilize a naturally occurring transport mechanism to deliver the agents to the lens cells.

Some agents described herein exist naturally in the untreated eye. Lipoic acid and cystine, for example, occur naturally in eye tissue. In general, a therapeutically effective amount of the exogenously administered agent is often at least about 1 or 2 orders of magnitude larger than the natural level of the agent. In one embodiment, the lipoic acid or derivative thereof is administered in a dose amount of up to about 1 mM. In one embodiment, the dose amount of lipoic acid or a derivative thereof is about 1 μM up to 1 mM, preferably about 0.25 mM to about 0.75 mM, or about 0.5 mM. In another embodiment, the dose amount of lipoic acid or derivative thereof is no more than 0.5 mM, 250 μM, 100 μM, 50 μM, 20 μM, or 10 μM. In another embodiment, cystine or a derivative thereof is administered in a dose amount of about 1 μM to about 20 μM. In yet another embodiment, the dose amount of cystine or a derivative thereof is no more than 20 μM, the limit of cystine solubility in aqueous solution, or no more than 15 μM, 12 μM, 10 μM, 7 μM, or 5 μM. The dose amount will depend on the route of administration as well as the age and condition of the patient. Similarly, the frequency of dosing will depend on similar factors as can be determined by one of ordinary skill in the art.

Efficacy has been demonstrated in vitro for specific exemplary dosing. FIG. 2 shows that the inelasticity increases by a factor of nearly 20 during the critical period from age 40 to 55 years. From current data, a 10 μM dose can decrease the inelasticity over 95% within a millimeter volume element (voxel). Extrapolation of these results to a volume element in the human lens suggests that using this treatment dose on a 55 year old person with a 10 kPA lens starting modulus value (see FIG. 2) could be reduced after treatment to a value of about 0.5 kPA (which then corresponds to a value typically seen with a 40 yr old person). FIG. 1 permits a conversion of these modulus values to optical amplitude: accommodative amplitude is normally reduced to almost 0 above 55 years, while a person at 40-45 years still exhibits around 4-5 diopters of accommodation.

The methods include preventative methods that can be performed on patients of any age. The methods also include therapeutic methods that can be performed on patients of any age, particularly patients that are at least 20, 25, 30, 35, 40, 45, 50, 52, 55, 57, 60, 70, 75, or 80 years of age.

IV. Pharmaceutical Compositions

In another embodiment, a pharmaceutical composition includes an agent as described herein and a pharmaceutically acceptable carrier. A “pharmaceutically acceptable carrier,” as used herein refers to pharmaceutical excipients, for example, pharmaceutically, physiologically, acceptable organic or inorganic carrier substances suitable for enteral or parenteral application that do not deleteriously react with the active agent. Suitable pharmaceutically acceptable carriers include water, salt solutions (such as Ringer's solution), alcohols, oils, gelatins, and carbohydrates such as lactose, amylose or starch, fatty acid esters, hydroxymethyl cellulose, and polyvinyl pyrrolidine. Such preparations can be sterilized and, if desired, mixed with auxiliary agents such as lubricants, preservatives, stabilizers, wetting agents, emulsifiers, salts for influencing osmotic pressure, buffers, coloring, and/or aromatic substances and the like that do not deleteriously react with the compounds of the invention.

The pharmaceutical composition may also contain one or more excipients as is well known in the art of pharmaceutical formulary. In one embodiment, the pharmaceutical composition is formulated for ocular use. That is, the pharmaceutically acceptable carrier and/or other excipients are selected to be compatible with, and suitable for, ocular use. Such carriers and excipients are well known in the art. The excipients may also be selected and/or formulated to improve the solubility of the compound. For example, the pharmaceutical composition can include one or more of emulsifiers, buffers, salts, preservatives, lubricants, polymers, solvents, and other known excipients for ocular pharmaceutical formulations. In one embodiment, the pharmaceutical composition includes an emulsifier and a buffered carrier such as Polysorbate 80 in HBSS (Hank's Balanced Salt Solution).

In one aspect, there is provided a pharmaceutical composition which includes a compound or pharmaceutically acceptable salt thereof in combination (e.g., in formulation) with a pharmaceutically acceptable excipient.

The compounds described herein can be formulated to achieve any delivery system known in the art such as immediate or sustained release delivery; systemic, ocular, or localized delivery; topical or injection delivery; prodrug or caged delivery systems, e.g., coumarin cages (as described, for example, in co-pending application U.S. Ser. No. 12/267,260), and the like.

Liquid form preparations include solutions, suspensions, and emulsions, for example, water or water/propylene glycol solutions. Aqueous solutions suitable for oral use can be prepared by dissolving the active component in water and adding suitable colorants, flavors, stabilizers, and thickening agents as desired. Aqueous suspensions suitable for oral use can be made by dispersing the finely divided active component in water with viscous material, such as natural or synthetic gums, resins, methylcellulose, sodium carboxymethyl cellulose, and other well-known suspending agents. Also included are solid form preparations that are intended to be converted, shortly before use, to liquid form preparations for oral administration. Such liquid forms include solutions, suspensions, and emulsions. These preparations may contain, in addition to the active component, colorants, flavors, stabilizers, buffers, artificial and natural sweeteners, dispersants, thickeners, solubilizing agents, and the like.

Some compounds may have limited solubility in water and therefore may require a surfactant or other appropriate co-solvent in the composition. Such co-solvents include: Polysorbate 20, 60, and 80; Pluronic F-68, F-84, and P-103; cyclodextrin; and polyoxyl 35 castor oil. Such co-solvents are typically employed at a level between about 0.01% and about 2% by weight.

Viscosity greater than that of simple aqueous solutions may be desirable to decrease variability in dispensing the formulations, to decrease physical separation of components of a suspension or emulsion of formulation, and/or otherwise to improve the formulation. Such viscosity building agents include, for example, polyvinyl alcohol, polyvinyl pyrrolidone, methyl cellulose, hydroxy propyl methylcellulose, hydroxyethyl cellulose, carboxymethyl cellulose, hydroxy propyl cellulose, chondroitin sulfate and salts thereof, hyaluronic acid and salts thereof, and combinations of the foregoing. Such agents are typically employed at a level between about 0.01% and about 2% by weight.

The compositions of the present invention may additionally include components to provide sustained release and/or comfort. Such components include high molecular weight, anionic mucomimetic polymers, gelling polysaccharides, and finely-divided drug carrier substrates, as known in the art.

The compounds can be administered to a lens by any route of administration including, but not limited to, topical, subtenons, subconjunctival, intracameral, intravitreal, or iontophoresis routes. In one embodiment, the agent can be delivered topically, e.g., via an eye drop, gel, ointment, or salve. In other embodiment, the compound can be delivered via an acute delivery system, e.g., using nanotubes, local injection, micro-injection, syringe or scleral deposition, or ultrasound.

Pharmaceutical compositions provided by the present invention include compositions wherein the active ingredient is contained in a therapeutically effective amount, i.e., in an amount effective to achieve its intended purpose. The actual amount effective for a particular application will depend, inter alia, on the condition being treated. For example, when administered in methods to treat cancer, such compositions will contain an amount of active ingredient effective to achieve the desired result (e.g. decreasing the number of cancer cells in a subject).

A. Dose Amounts

In one embodiment, the active agent is present in the pharmaceutical composition in an amount of about 0.1% to about 10% by weight, more specifically about 0.25% to about 10%, about 0.5% to about 10%, about 1% to about 8%, about 3% to about 7%, about 2% to about 5%, about 5% to about 7%, or about 5%. In another embodiment, the active agent is present in the pharmaceutical composition in an amount about 1 μM up to 1 mM, preferably about 0.25 mM to about 0.75 mM, or about 0.5 mM.

In some embodiments, a relatively low dose is called for. One such circumstance may be a preventative composition where the objective is to prevent rather than reverse oxidative damage. Another circumstance may be a priming or starting dose that would be titrated upward according to the subject's responsiveness and treatment objectives. In some embodiment, the active agent is present in an amount of about 0.1% to about 5%, about 0.1% to about 3%, about 0.1% to about 1%, about 1% to about 3%. In some embodiments, the active agent is present in an amount of less than about 250 μM, about 5 μM to about 250 μM, or about 10 μM to about 100 μM.

The dosage and frequency (single or multiple doses) of compound administered can vary depending upon a variety of factors, including route of administration; size, age, sex, health, body weight, body mass index, and diet of the recipient; nature and extent of symptoms of the disease being treated; presence of other diseases or other health-related problems; kind of concurrent treatment; and complications from any disease or treatment regimen. Other therapeutic regimens or agents can be used in conjunction with the methods and compounds of the invention.

Therapeutically effective amounts for use in humans may be determined from animal models. For example, a dose for humans can be formulated to achieve a concentration that has been found to be effective in animals. The dosage in humans can be adjusted by monitoring presbyopia in the human subject and adjusting the dosage upwards or downwards, as described above.

Dosages may be varied depending upon the requirements of the subject and the compound being employed. The dose administered to a subject, in the context of the present invention, should be sufficient to effect a beneficial therapeutic response in the subject over time. The size of the dose also will be determined by the existence, nature, and extent of any adverse side effects. Generally, treatment is initiated with smaller dosages, which are less than the optimum dose of the compound. Thereafter, the dosage is increased by small increments until the optimum effect under circumstances is reached. Dosage amounts and intervals can be adjusted individually to provide levels of the administered compound effective for the particular clinical indication being treated. This will provide a therapeutic regimen that is commensurate with the severity of the disease state of the subject.

The ratio between toxicity and therapeutic effect for a particular compound is its therapeutic index and can be expressed as the ratio between LD₅₀ (the amount of compound lethal in 50% of the population) and ED₅₀ (the amount of compound effective in 50% of the population). Compounds that exhibit high therapeutic indices are preferred. Therapeutic index data obtained from cell culture assays and/or animal studies can be used in formulating a range of dosages for use in humans. The dosage of such compounds preferably lies within a range of plasma concentrations that include the ED₅₀ with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration utilized. See, e.g. Fingl et al., In: THE PHARMACOLOGICAL BASIS OF THERAPEUTICS, Ch. 1, p. 1, 1975. The exact formulation, route of administration, and dosage can be chosen by the individual physician in view of the patient's condition and the particular method in which the compound is used.

B. Co-Administration of Additional Active Agents

The compounds described herein can be used in combination with one another, with other active agents known to be useful in ocular disease, or with adjunctive agents that may not be effective alone, but may contribute to the efficacy of the active agent. For example, adjunctive agents might include one or more amino acids or choline to enhance the efficacy of the active agent. The combinations can be advantageous, e.g., in reducing metabolic degradation.

The term “co-administer” means to administer more than one active agent, such that the duration of physiological effect of one active agent overlaps with the physiological effect of a second active agent. In some embodiments, co-administration includes administering one active agent within 0.5, 1, 2, 4, 6, 8, 10, 12, 16, 20, or 24 hours of a second active agent. Co-administration includes administering two active agents simultaneously, approximately simultaneously (e.g., within about 1, 5, 10, 15, 20, or 30 minutes of each other), or sequentially in any order. In some embodiments, co-administration can be accomplished by co-formulation, i.e., preparing a single pharmaceutical composition including both active agents. In other embodiments, the active agents can be formulated separately. In another embodiment, the active and/or adjunctive agents may be linked or conjugated to one another.

Without being bound by theory, it is believed that the administration of an active agent, e.g., lipoic acid or a derivative thereof, and an adjunctive agent such as choline, can be particularly advantageous in a conjugated form. The conjugate compound be applied to the cornea, and penetration is achieved due to the bi-phasic (water and lipid soluble) nature of the conjugate compound. As the conjugate goes through the cornea, naturally present esterases (enzymes) separate lipoic acid from choline. The lipoic acid (now a pro-drug) in the aqueous bathes the lens and enters the lens epithelial cells (due to low molecular weight and size), and there is reduced by any one of several oxido-reductases (enzymes such as thioredoxin and thioltransferase) to form dihydrolipoic acid. Dihydrolipoic acid now has two extra hydrogen atoms to donate to a disulfide complex (e.g., protein disulfide PSSP), separating the two sulfur atoms into sulfhydril molecules (e.g., protein cysteine residues PSH with free SH groups) thus breaking the inter-cytosol protein cross-links. Breaking these cross-link is what reduces the lens stiffness. Once donation of the hydrogen atoms to the sulfur atom, the dihydrolipoic acid becomes lipoic acid and is available for recycling in the cell to become dihydrolipoic acid or converted to a natural degraded by product thiolactone and excreted.

C. Co-Administration with a Biochemical Energy Source

In one embodiment, a reducing agent, such as one of the compounds described herein, is co-administered with a biochemical energy source. A biochemical energy source facilitates reduction by participating as an intermediate of energy metabolic pathways, particularly the glucose metabolic pathway. Exemplary intermediates of this pathway are depicted by, e.g., Zwingmann, C. et al. 2001. 13C Isotopomer Analysis of Glucose and Alanine Metabolism Reveals Cytosolic Pyruvate Compartmentation as Part of Energy Metabolism in Astrocytes. GLIA 34:200-212. Exemplary biochemical energy sources include, e.g., glucose or a portion thereof (e.g., glucose-6-phosphate (G6P)), pyruvate (e.g., ethyl pyruvate), NADPH, lactate or derivative thereof G6P may be favored over glucose since a formulation including glucose may further benefit from the addition of preservatives. In one embodiment, the biochemical energy source is an intermediate in a cytosolic metabolic pathway. Exemplary cytosolic pathway intermediates include, e.g., glucose, pyruvate, lactate, alanine, glutamate, and 2-oxoglutarate. In another embodiment, the biochemical energy source is an intermediate in a mitochondrial metabolic pathway. Exemplary mitochondrial pathway intermediates include, e.g., pyruvate, TCA-cycle intermediates, 2-oxoglutarate, glutamate, and glutamine. In one embodiment, the biochemical energy source is pyruvate compound (e.g., ethyl pyruvate). In another embodiment, the biochemical energy source is alanine.

In one embodiment, the agent is co-administered with glucose-6-phosphate (G6P), NADPH, or glucose. In one embodiment, the agent is activated by an endogenous chemical energy, e.g., endogenous glucose. For example, endogenous glucose can activate lipoic acid or a derivative thereof to dihydrolipoic acid (DHLA) or a corresponding derivative thereof.

Examples Example 1 In vitro Efficacy Studies

Increase in Elasticity: Pairs of mouse lenses were incubated in medium 200 supplemented with an antibiotic, an antimycotic, in the presence or absence of lipoic acid (concentrations ranging from 0.5 μM to 500 μM) for 8-15 hours. Each lens was removed from medium, weighed, and photographed on a micrometer scale. A coverslip of known weight (0.17899±0.00200 g) was placed on the lens, and the lens was photographed again on the micrometer scale. The diameter of each lens with and without the coverslip was determined from the photographs. The change in lens diameter produced by the force (coverslip) was computed ΔD=(D_(withcoverslip)−D_(withoutcoverslip)). The results (FIG. 4, ‡) indicate that lipoic acid at concentrations ≧9.6 μM caused a statistically significant increase in ΔD, p<0.0001.

Decrease in disulfide bonds: Lipoic acid at concentrations ≧9.6 μM caused a statistically significant decrease in protein disulfides in the mouse lenses where there was a significant increase in ΔD (FIG. 4). Mouse lenses were homogenized in a denaturing buffer containing a fluorescent alkylating agent to modify the free SH groups. After removing the alkylating agent homogenates were reduced and alkylated with a different fluorescent alkylating agent. Absorption spectra of the modified proteins were used to calculate free protein SH and protein SS groups. The results are shown in FIG. 5.

Example 2 Synthesis of (R)-Lipoamide

NHS ester of (R)-lipoic acid. The NHS ester of (R)-lipoic acid was synthesized as described in Scheme 1 following.

A solution of lipoic acid (25.6 g, 124 mmol), N-hydroxysuccinimide (15.6 g, 136 mmol), and EDC (26.1 g, 136 mmol) in anhydrous CH₂Cl₂ (300 mL) was stirred overnight at room temperature. The reaction mixture was diluted with ethyl acetate (500 mL) and washed with H2O (500 mL), saturated aqueous NaHCO₃ (500 mL), saturated aqueous NaCl (500 mL) and dried (MgSO₄). The drying agent was removed by filtration and the filtrate was concentrated to dryness giving the product as a yellow sold (35.4 g, 94%).

(R)-Lipoamide. (R)-lipoamide was synthesized as described in Scheme 2 following.

A solution of the NHS ester (2.7 g, 8.9 mmol) in anhydrous CH₂Cl₂ (50 mL) was cooled in a dry ice acetone bath. Ammonia was condensed into the reaction mixture over a period of 1-2 hours, then the reaction mixture was allowed to warm to room temperature overnight and diluted with CH₂Cl₂ (50 mL). Water (100 mL) was added and the mixture was stirred for 20 minutes. The phases were separated. The organic phase was washed with saturated aqueous NaCl (100 mL) and dried (Na₂SO₄). The drying agent was removed by filtration and the filtrate was concentrated to dryness giving the product as a yellow microcrystalline sold (1.56 g, 85%).

Example 3 Synthesis of an Arginine-Lipoic Acid Conjugate (“LA-Arg”)

Pentafluorophenyl ester of (R)-lipoic acid. The pentafluorophenyl ester of (R)-lipoic acid was synthesis as described in Scheme 3 following.

Solid EDC (1.04 g, 5.4 mmol) was added at once to a solution of lipoic acid (1.0 g, 4.8 mmol), and pentafluorophenol (1 g, 5.4 mmol) in anhydrous CH₂Cl₂:DMF (14 mL; (6:1)). The solution was stirred overnight at room temperature then concentrated to dryness. Flash column chromatography (SiO₂, 100% DCM) afforded the product as a clear, thick yellow oil (1.67 g, 94%).

LA-Arg. The arginine-lipoic acid conjugate was synthesis as described in Scheme 4 following.

L-Arginine (530 mg, 3.1 mmol) was added at once to a solution of the Pfp ester (1.34 g, 3.6 mmol) in anhydrous DMF (4 mL). The reaction mixture was stirred at room temperature for 48 hours. Insolubles were isolated by vacuum filtration and the filter cake was washed with CHCl₃ (20 mL). The material was dried in vacuo overnight giving the product as a pale yellow solid (340 mg, 26%).

Example 4 Syntheses of Lipoic Acid Choline Ester

Lipoic acid choline ester was prepared according to the following synthetic route. Choline salts of alternative reducing agents can be similarly prepared by making the appropriate reagents substitutions. Also, one of ordinary skill in the art would recognize that these syntheses are provided as guidance and that reagents, conditions, amounts, temperatures, and the like may be modified without departing from the general synthetic pathway.

Step 1:

(R)-2-(dimethylamino)ethyl 5-(1,2-dithiolan-3-yl)pentanoate. A solution of DCC (11 g, 53 mmol) in anhydrous CH₂Cl₂ (20 mL) was added with stirring over 10-20 minutes to a cold (0° C.) solution of R-lipoic acid (10.0 g, 48.5 mmol), N,N-dimethylethanolamine (14.5 mL, 145 mmol, 3 eq.), and DMAP (600 mg, 4.9 mmol) in anhydrous CH₂Cl₂ (50 mL). Following complete addition, the cold bath was removed. After 18 hours at room temperature, all volatiles were removed under reduced pressure, and the resulting residue was purified by flash column chromatography (SiO₂, 2% MeOH in CH₂Cl₂) providing the desired product as a clear yellow oil (10.6 g, 79%). All data consistent with values reported in the literature. (See Courvoisier C. et al. 2006. Synthesis and effects of 3-methylthiopropanoyl thiolesters of lipoic acid, methional metabolite mimics. Bioorganic Chemistry 34(1):49-58.)

Step 2:

(R)-2-(5-(1,2-dithiolan-3-yl)pentanoyloxy)-N,N,N-(trimethyl)ethylammonium iodide. Methyl iodide (0.55 mL, 9.0 mmol) was added to a solution of the amine (2.5 g, 9.0 mmol) in anhydrous CH₂Cl₂ (20 mL). The reaction mixture was stirred overnight and slowly poured into diethyl ether (250 mL) with vigorous stirring. The choline salt was isolated by filtration as a free-flowing pale, yellow sold (3.7 g, 98%).

Example 4b One-Step Synthetic Route

Example 5 Eye Drop Formulation of Lipoic Acid Choline Ester

The following eye drop formulation was prepared using lipoic acid choline ester as the active agent.

Formula A

Concentration Ingredient % by weight Purpose Lipoic acid choline ester 5.0 Active agent Ethyl pyruvate 0.1 Energy source Sodium phosphate 0.269 Buffer monobasic monohydrate, USP Sodium phosphate 0.433 Buffer dibasic anhydrous, USP Sodium chloride 0.5 Tonicity agent Hydroxypropylmethylcellulose 0.2 Viscosity agent (HPMC), USP De-ionized, pyrogen free water to 100 mL Solvent Formula B

Concentration Ingredient % by weight Purpose Lipoic acid choline ester 5.0 Active agent Alanine 0.5 Stabilizer Sodium phosphate 0.269 Buffer monobasic monohydrate, USP Sodium phosphate 0.433 Buffer dibasic anhydrous, USP Sodium chloride 0.5 Tonicity agent Hydroxypropylmethylcellulose 0.2 Viscosity agent (HPMC), USP De-ionized, pyrogen free water to 100 mL Solvent

The eye drop formulation has a pH of 7.0.

The pharmaceutical formulation may be diluted to 100 ml filtered water (e.g., Millex syringe filter (0.45 micron 33 mm). The pharmaceutical composition may be packaged for multi-dose administration, e.g., 2-7 mL (e.g., 5 mL) eyedropper bottle with screw lid dropper.

The examples given above are merely illustrative and are not meant to be an exhaustive list of all possible embodiments, applications, or modifications of the invention. Thus, various modifications and variations of the described methods and systems of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes of carrying out the invention which are obvious to those skilled in the chemical arts or in the relevant fields are intended to be within the scope of the appended claims.

The disclosures of all references and publications cited above are expressly incorporated by reference in their entireties to the same extent as if each were incorporated by reference individually. 

What is claimed is:
 1. A method of treating presbyopia comprising administering to a subject a compound having the structure of Formula I or a pharmaceutically acceptable salt thereof:

wherein at least one of X and Y is sulfur, and the other is sulfur, selenium, or a sulfonic group; R₁₉ is substituted or unsubstituted alkylene; R₂₀, R₂₁, R₃₀, and R₃₁ are each independently hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted heterocycloalkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl; wherein R₃₀ and R₃₁ may optionally be joined together or together form a single bond; Z is N or O; and m is 0 or 1, wherein if Z is O, then m is 0, and if Z is N, then m is 1, and wherein the compound is not 5-(1,2-dithiolan-3-yl)pentanoic acid.
 2. The method of claim 1, wherein one of X and Y is sulfur, and the other is sulfur or selenium.
 3. The method of claim 1, wherein X and Y are both sulfur.
 4. The method of claim 1, wherein R₁₉ is unsubstituted alkylene.
 5. The method of claim 4, wherein R₁₉ is C₄ alkylene.
 6. The method of claim 5, wherein the compound has a structure of Formula III(R):


7. The method of claim 6, wherein the compound is:


8. The method of claim 6, wherein the compound has a structure of Formula IVB

wherein R₂₉ is the side chain of an alpha amino acid.
 9. The method of claim 8, wherein the compound is:


10. The method of claim 5, wherein the compound has a structure of Formula VI(R):


11. The method of claim 10, wherein R₂₁ is alkyl.
 12. The method of claim 11, wherein said compound has the structure


13. The method of claim 10, wherein the compound is:


14. The method of claim 1, wherein the compound is a tromethamine salt.
 15. The method of claim 1, wherein the compound is:

and wherein Z⁻ is any pharmaceutically acceptable counterion.
 16. The method of claim 15, wherein Z⁻ is a sulfate, methanesulfonate, nitrate, maleate, acetate, citrate, fumarate, tartrate, succinate, benzoate, glutamate, chloride, bromide, or iodide.
 17. The method of claim 16, wherein the compound is:


18. The method of claim 16, wherein Z⁻ is a tartrate. 